The present invention relates to an image forming apparatus and an image forming method and, more particularly, to an image forming apparatus such as a digital copying machine for temporarily storing image data corresponding to a document image and forming an image on a paper sheet based on the stored image data, and an image forming method applicable to the image forming apparatus.
A digital copying machine for optically reading a document image, creating image data corresponding to the document image, temporarily storing the image data, and forming an image on a paper sheet in predetermined timing based on the stored image data, has recently been put into practical use.
The digital copying machine comprises an automatic document feeding unit in which a plurality of original documents can be set, for feeding the set documents to a predetermined position of a document table in predetermined timing, a scanner section for reading an image of each of the documents located in the predetermined position of the document table and converting information of the image into image data, an image memory for temporarily storing the image data of the document image read by the scanner section, a paper feeding unit in which a plurality of paper sheets can be held as recording mediums, for feeding the paper sheets one by one, a printer section for forming an image on each of the paper sheets fed from the paper feeding unit based on the image data stored in the image memory, and a reversing mechanism including a stacking section for temporarily stacking the paper sheets each having an image formed on its one side, for reversing the paper sheets in predetermined timing and resupplying them to the printer section.
Of digital copying machines as described above, there is one having a double-sided image forming mode which is predicated on a so-called paper stack system in which an image is formed on a single side of each of paper sheets and such paper sheets are stored temporarily. In the double-sided image forming mode, an image is formed on one side of each of paper sheets supplied from the paper feeding unit based on image data stored in the image memory in the printer section, and these paper sheets are stacked in sequence in the stacking section. The stacked paper sheets are reversed in predetermined timing and supplied to the printer section again. An image is then formed on the other side of each of the paper sheets based on the image data, and these paper sheets are ejected.
The above double-sided image forming mode employing a paper stack system is a function peculiar to a digital copying machine and thus allows an image to be formed quickly on both sides of a paper sheet.
In the double-sided image forming mode, if a sheet with an image only on its one side remains in the stacking section of the reversing mechanism though all image data is output from the image memory to complete the double-sided image forming mode, there is a strong possibility that images are not formed in correct order on both sides of each paper sheet.
The above phenomenon occurs when two or more paper sheets are supplied together from the paper feeding unit to the printer section. For example, when two paper sheets are supplied at once, an image is formed on a single side of only one of them and then the two paper sheets are stacked in the stacking section of the reversing mechanism. Since, however, the number of the paper sheets is counted as one on the image forming apparatus side, one paper sheet still remains in the stacking section even the other paper sheet is resupplied from the stacking section to the printer section. Consequently, images are not formed on both sides of a paper sheet in correct order.
Similarly, there is a strong possibility that images will not be formed on both sides of a paper sheet in correct order even when no sufficient paper sheets remain in the stacking section of the reversing mechanism before the double-sided image forming mode is completed.
This phenomenon occurs when two or more paper sheets are resupplied from the stacking section to the printer section. Assume two paper sheets are stacked in the stacking section. If the two paper sheets are resupplied to the printer section at once, the stacking section is emptied when one image forming operation is completed. Consequently, images are not formed on both sides of a paper sheet in correct order.
In the foregoing image forming apparatus having a double-sided image forming mode employing a paper stack system, it is likely that images cannot be formed on both sides of a paper sheet in correct order when a paper sheet remains in the stacking section of the reversing mechanism after the double-sided image forming mode is completed or when the stacking section is emptied before the mode is completed. For this reason, the double-sided image forming mode causes a problem of low reliability though the mode is a function peculiar to an image forming apparatus, especially a digital copying machine.
The present invention has been developed in order to resolve the above problem and its object is to provide an image forming apparatus capable of forming images on both sides of a recording medium in correct order and having a double-sided image forming mode with high reliability, and an image forming method applicable to the image forming apparatus.
According to a first aspect of the present invention, there is provided an image forming method comprising:
forming an image on one side of each of a plurality of recording mediums based on image data edited in predetermined output order;
temporarily stacking the plurality of recording mediums, each bearing the image on one side thereof, in a stacking section, the recording mediums being stacked in a reverse state;
forming an image on another side of each of the recording mediums stacked in the reverse state based on the image data in predetermined timing, and then ejecting the recording mediums outside; and
ejecting a recording medium remaining in the stacking section outside when all images corresponding to the image data have been formed on the plurality of recording mediums.
According to a second aspect of the present invention, there is provided an image forming method comprising:
a first step of forming an image on one side of each of a plurality of recording mediums based on image data edited in predetermined output order, and temporarily stacking the plurality of recording mediums in a stacking section, the recording mediums being staked in a reverse state;
a second step of forming an image on another side of each of the recording mediums stacked in the reverse state based on the image data in predetermined timing, and ejecting the recording mediums outside; and
a third step of executing the first step again in a case where no recording medium remains in the stacking section before all images corresponding to the image data are formed on the plurality of recording mediums.
According to a third aspect of the present invention, there is provided an image forming apparatus comprising:
image forming means for forming an image on a recording medium based on image data;
stacking means for temporarily stacking the recording medium in a reverse state, an image being formed on one side of the recording medium by the image forming means;
supplying means for supplying the recording medium stacked in the stacking means to the image forming means in predetermined timing;
sensing means for sensing whether the recording medium is present in the stacking means; and
control means having a double-sided image forming mode in which the image forming means forms images corresponding to image data on first and second sides of each of a plurality of recording mediums, the control means executing the double-sided image forming mode once again in a case where the sensing means senses that no recording medium remains in the stacking means before all the images corresponding to the image data are formed on the recording mediums stacked in the stacking means in the double-sided image forming mode.
According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising:
image formation means for forming an image on recording mediums based on image data;
stacking means for temporarily stacking the recording mediums, each bearing the image formed on one side thereof by the image formation means, the recording mediums being stacked in a reverse state;
supplying means for supplying the recording mediums stacked in the stacking means to the image formation means in predetermined timing;
sensing means for sensing whether a recording medium is present in the stacking means;
ejecting means for ejecting the recording mediums outside; and
control means having a double-sided image forming mode in which the image forming means forms images corresponding to image data on first and second sides of each of a plurality of recording mediums, the control means controlling the ejecting means to eject a recording medium outside in a case where the sensing means senses that the recording medium is present in the stacking means when all images corresponding to the image data have been formed on the plurality of recording mediums stacked in the stacking means in the double-sided image forming mode.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.